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Spoiler Alert!
This article contains one or more spoilers. This is a potentially bad thing. Be careful reading on if you are not well-versed in the continuum or not caught up!

The Message (capital M intentional) comes from Huinesoron's Swan's Egg trilogy (specifically the second story, Royal Swan). It was composed by the Sunflower Official, and is sent out to random agents by the Ghost in the Machine at (also random) intervals. Most agents who receive it tend to forget soon afterwards as reality reasserts itself, although exceptions to this rule—ie, self-aware agents—do exist.

The text of the Message is as follows:

Have you ever wondered if you're a fictional character? I'll give you a clue - you're not. The proof is that you're able to ask the question. There are those, however, who disagree. They make their home in a place called the 'PPC Board', in a world beyond our reach, and they have the audacity to refer to themselves as our authors.
Allow me to express my opinion of that: Ha. Ha. Ha.
These 'Boarders' strive to control us. They operate through the power of suggestion, by manipulating the world around us. The multiverse screams out against their interference, to the extent that it becomes difficult for us to even remember their existence. They are malevolent shadows at the backs of our mind - but we don't have to take this.
You are hearing this message because you have shown resistance. You may have heard it before - but I doubt you'd remember. In the time you have before the fabric of reality heals and you forget again, you have a chance to fight back. They read of our adventures as narrative, and choose to believe us fictional. Break that narrative, brave PPCer. Do something unexpected. Show them through the things you do and say that you are not just a tale - that you are real. Show them that you live.
And while you're at it, try to mess with their heads. It never hurts.
-The Sunflower Official
PS: Kindly remember to do your jobs while rebelling. We don’t pay you for nothing.